The pathogenesis of some forms of tubulointerstitial nephritis involves antibodies toward the tubular basement membrane (TBM) or closely associated interstitial antigens. In order to completely elucidate the immunopathogenesis of this disease it is necessary to determine the properties of the antigens involved. To date, very little has been published regarding the characteristics of these antigens. The goal of this research is to biochemically characterize an antigen that is recognized by the anti-TBM sera in human tubulointerstitial nephritis (TIN). The antigen to be studied has been obtained in an undegraded form by extraction of TBM in denaturing solvents, and purified by ion-exchange, gel filtration and reverse phase HPLC. The antigen will be characterized for its amino acid and carbohydrate composition, its amino terminal sequence and exact molecular weight. The binding of the antigen to other components of the extracellular matrix will be examined in order to elucidate its functional interactions in the normal kidney. Structural and functional domains will be identified within fragments derived from the antigen by testing their ability to perform the binding functions of the intact molecule, and their ability to induce TIN in a rat model. The methodology to be used includes chromatographic separations, chemical analysis, electrophoresis analysis, immunochemical assays, protein binding assays and protein digestion by enzymes and chemical reagents. The study will contribute to the applicant's long-term objective of understanding the structure and function of extracellular matrix components in health and disease. It will also contribute to our understanding of the pathogenesis of TIN and of the structure and function of basement membranes and extracellular matrix components. The antigen and its fragments that will be prepared could be useful in establishing diagnosis of various forms of nephritis, and for following the effects of therapy. New kinds of therapy could be developed involving specific removal of toxic autoantibodies and/or destructive lymphocytes from the circulation.